In vitro comparison between four variants of Aujeszky's disease virus.

Four Aujeszky's disease (pseudorabies) virus variants were characterized in vitro by investigation of their resistance to heat at 48 degrees C, sensitivity to trypsin and ability to replicate in pig alveolar macrophages, two of these variants (Ls-1 and Ls-2) were cloned previously from a single isolate of virus and showed differing pathogenicity for pigs; the virulent Stanley strain; and the non-virulent NIA-4 strain were included for comparison. Heat treatment produced slight decreases in infectivity but no significant differences were observed in the rates of inactivation. Both Ls-1 and Ls-2 were significantly more sensitive to trypsin treatment than the other two. The comparison of progeny virus titres after replication in alveolar macrophages allowed further differentiation among variants. Ls-1 and Ls-2 had similar titres in cultures infected with high virus input but in cultures infected with low virus input (0.1 TCID50/cell) Ls-1 produced higher titre. The difference in titres at 48 h post-infection was statistically significant (P less than 0.05). The cytopathogenicity for macrophages of the strains was correlated with their virulence for pigs, Stanley strain being the most cytopathogenic and NIA-4 the least.

Classical swine fever: virulence and tissue distribution of a 1986 English isolate in pigs.

Following the recurrence of classical swine fever in the United Kingdom in 1986, a virus isolated from a single outbreak was studied. A major factor in the spread of this disease is considered to be the presence of infectious virus in tissues taken from animals at certain stages of infection, although their condition may escape detection by routine inspection either before or after slaughter. Intranasal inoculation of the isolate into eight-week-old pigs reproduced the acute form of the disease. The pigs were killed or died between seven and 25 days after inoculation. The virus concentration was determined in a wide range of tissues taken at different stages of infection. Infectious virus was present at high concentrations in all the tissues taken and at all stages of infection. Any porcine tissue is therefore a potential source of infection even when it is taken either before the animal displays detectable signs of disease of after it develops serum neutralising antibodies.

Studies of transplacental and perinatal infection with two clones of a single Aujeszky's disease (pseudorabies) virus isolate.

The effect of Aujeszky's disease virus (ADV) infection in the last third of gestation was studied using two clones from an ADV isolate. Twelve sows were infected with one or other clone at 85 +/- 1 days of gestation. The dose of infection was 5 X 10(6) TCID50 per sow. The clinical and serological responses to the infection were different. One clone, Ls-1, produces a severe and acute illness. The course of the disease went from 9 to 14 days while the other clone, Ls-2, caused a mild or silent infection and for a shorter time. Transplacental infection occurred in only one sow which had been infected with Ls-2. The litter consisted of 8 mummified fetuses. Sows infected with Ls-1 produced piglets or mummified fetuses that were virus-negative. Perinatal infection was found in litters from both groups. Colostrum-deprived piglets that did not have postpartum contact with the sow, produced specific antibodies, 2 out of 6 born to sows infected with Ls-1 and 1 out of 4 born to sows infected with Ls-2. The antibody titers in colostrum-fed piglets were related to the extent of clinical response of the sows to the infection. Litters born to sows infected with Ls-1 had mean SNT titers from 1/12 to 1/112 while litters born to sows infected with Ls-2 showed titers of 1/2 or less than 2.

A genetic, pathological and virological study of congenital hypotrichosis and incisor anodontia in cattle.

Two Friesian cows, half-sibs by a common dam, produced four bull calves with severe congenital hypotrichosis and incisor anodontia and three normal heifers by six unrelated Holstein, Friesian, Devon and Hereford bulls. The two dams, and their dam, had coats of a short, stubbly nature and the pigmented areas appeared rusty grey rather than black. Pathological examination of skin samples taken from multiple standardised sites from two of the affected calves showed a reduction in the number of large first-formed hair follicles. Smaller calibre hair follicles were present but, unlike those of normal neonatal calves, all were in the telogen (inactive) phase. Although the herd was infected with bovine virus diarrhoea virus there was no convincing evidence that the virus was implicated in the pathogenesis of these cases of congenital hypotrichosis with incisor anodontia. The family breeding information on the few severely affected and normal progeny and mildly affected and normal parents may be explained by the genetic hypothesis of an X-linked incompletely dominant gene.

The application of monoclonal antibody panels to characterize pestivirus isolates from ruminants in Great Britain.

Monoclonal antibodies were prepared against bovine virus diarrhoea virus and hog cholera virus. They were used to test 101 field isolates of ruminant pestivirus in a simple binding assay using an indirect immunoperoxidase label on fixed cell cultures. The monoclonals were divided into three panels: (1) pestivirus group specific, (2) hog cholera specific, (3) selectively reactive with ruminant pestiviruses. The reaction patterns with panel 3 were analyzed by a computer spreadsheet to determine the percentage match with seven reference patterns. Field viruses could be divided into two main groups. Group A consisted of 73 (87%) of the 84 bovine isolates and three (19%) of the 16 ovine, and was reactive with 40% or more of panel 3. Group B showed only limited reactivity with panel 3 and comprised 13/16 (81%) of the ovine (border disease) isolates together with the remaining 11 (13%) bovine viruses.

The control of bovine viral diarrhoea virus infection.

In this paper, current ideas concerning the epidemiology of BVD virus infection are reviewed briefly, together with its possible economic implications. The different types of control strategies are considered. Problems associated with vaccination are discussed.

BVD virus infection: prospects for control.

Losses resulting from pestivirus infections in cattle are of considerable importance to the livestock industry yet, until relatively recently, they have been poorly understood. The escalation of research effort in this field has started to clarify the pathogenesis and epidemiology of the associated diseases but the evolution of understanding is far from complete. Sufficient information exists to indicate the means by which pestivirus infection is introduced to and maintained in populations of cattle. A brief review of current knowledge is given placing particular emphasis on the role played by persistent infections which have resulted from intrauterine infection. The crux of the problem of control is seen to be the avoidance of fetal infection in early gestation. Ways of achieving this which include the immunisation of female cattle with live or inactivated virus vaccines are discussed and areas requiring further work are indicated.

Classical swine fever and its diagnosis: a current view.

Classical swine fever is one of the most important viral diseases of pigs and a major source of loss for pig producers worldwide. The disease was eradicated from Great Britain in 1966 and, apart from a single incident in 1971, has not reappeared. A major epizootic started in Europe in 1982-83 and continued through 1984. Extra vigilance is necessary in order to detect any introduction of infection. The disease takes several forms apart from the dramatic disease described in textbooks. These include mild and chronic disease and reproductive losses of various types. Mild disease is a feature of the epizootic in Europe at present. Diagnostic methods are outlined. Diagnosis is frequently difficult and requires laboratory help. The selection and handling of specimens for the laboratory is critical to the success of diagnosis.

Influence of vaccination on Aujeszky's disease virus and disease transmission.

Parenteral vaccination of fattening pigs with either modified live or inactivated Aujeszky's disease virus did not prevent infection with field strain virus or the development of clinical disease. The duration and severity of the clinical syndrome was, however, reduced and vaccinated pigs did not suffer the severe weight loss and high mortality experienced by non-vaccinated pigs in the acute phase of disease. The range of tissues in which challenge virus replication took place was more restricted in vaccinated animals and the concentration of virus in infected tissues was reduced. Vaccination shortened the duration of field virus excretion and carriage in the tonsil. Replication of modified live vaccine virus was restricted to the site of inoculation in the neck and associated lymph nodes for two days after vaccination and it was not excreted by vaccinated pigs. Attempts to infect pigs by feeding them tissues taken from non-vaccinated or vaccinated pigs soon after challenge infection were unsuccessful.

The influence of a family history of CHD risk factors on serum lipoprotein levels in black children and adolescents.

This study evaluated the influence of a family history of coronary heart disease (CHD) and CHD risk factors on the total serum cholesterol/high density lipoprotein (TChol/HDL) and the low density lipoprotein/HDL (LDL/HDL) ratios of 84 black children (ages 7-11 years) and adolescents (ages 12-15 years). Fasting lipid determinations were measured on all subjects. A questionnaire was administered to each subject's parent to determine the frequency of myocardial infarction, heart disease, hypertension, stroke, atherosclerosis, diabetes, and obesity in first- and second-degree blood relatives. Based on three-way analysis of variance tests, significant stroke and age, diabetes and age, and obesity and age interactions in TChol/HDL and LDL/HDL were found. There was also an obesity and age and sex interaction effect on T.Chol/HDL. The results indicated that a family history of stroke, diabetes, or obesity can have an unfavorable effect on the TChol/HDL and LDL/HDL ratios in black adolescents.

Influence of temperature on the growth in cell culture of malignant catarrhal fever virus.

The growth characteristics of malignant catarrhal fever (MCF) virus in bovine thyroid cultures were affected by incubation temperature. The cytopathic effect at 37 degrees C was predominantly syncytial and little or no cell-free virus could be detected. At 32 degrees to 34 degrees C foci of rounded refractile cells were observed, and this was accompanied by an increase in the amount of cell-free virus found in culture fluids. Growth curve studies with one low passage isolate of MCF virus showed that optimum yields of cell-free virus were obtained at 32 degrees to 34 degrees C and survival curves at 32 degrees and 37 degrees C indicated that this was a result of the relatively short half life of the virus at the higher temperature. A number of other benefits resulted from the use of lowered incubation temperature and these are discussed with reference to in vitro work with the virus.